The world Nadella describes is also one in which Microsoft, after years of chasing the tectonic shift to mobile devices, can lead again — by helping other businesses navigate the shift to mobile devices that threatened to derail Microsoft itself. Former CEO Steve Ballmer saw Windows as the center of the world, and the story of Microsoft was the operating system’s unstoppable march around the globe. At a small news event in San Francisco today, Nadella formally acknowledged a changed world: one where our computing is more likely to be done on a device made by a competitor than one branded with the Microsoft logo. "There is no trade-off; it’s reality for us," Nadella said as he pledged to bring Microsoft services to customers whatever platform they use. "What motivates us is the realities of our customers."